This invention relates generally to printed circuit cards and, more particularly, to printed circuit cards that comprise computer printer and video game cartridges and that include memory chips that serve to configure such microprocessor based printers, video game computers, and other mainframes. For example, many computer printers can accommodate up to twenty or more different character font cartridges while only providing receptacles for two of these font cartridges at any given time. It is therefore frequently necessary to change font cartridges between the printing of documents in order to access different character font sets that allow the user to take advantage of the flexibility in character font selection, etc. that is within the capability of the printer. Ideally, such plug-in cartridges should not be plugged into or removed from the printer or game computer mainframes with which they operate without first removing power to the mainframe. In practice, however, users of mainframes such as printers and game computers oftentimes either inadvertently or intentionally insert or remove cartridges without first turning off power to the mainframe. This typically has the effect of causing a glitch to occur on the memory address and data bus signal lines that couple the cartridge to the mainframe, thereby causing the microprocessor located in the mainframe to be set to an unknown state that may very well interrupt its normal and expected operation. In the worst case, permanent damage may result to electrical components located in either the cartride or the mainframe.
One prior art solution to this problem has been to implement bus buffers on all signal lines coupling the plug-in cartridge to the mainframe, thus electrically isolating the electrical components located in the plug-in cartridge from the microprocessor located in the mainframe. This solution is disadvantageous in that it is costly, requires additional shielding to accommodate radio frequency interference constraints, and increases the time required for communication between the microprocessor and the plug-in cartridge to take place.
It is therefore the principal object of the present invention to provide a printed circuit card for use in plug-in cartridges of the type that are typically employed in printer and game computer mainframes having provision for automatically generating a reset pulse every time such a cartridge is plugged into or removed from the mainframe with which it operates. Applying such a reset pulse on the microprocessor reset signal line has the effect of setting the microprocessor to a known state just as if operating power to the microprocessor had been removed and then reapplied. This object is accomplished in accordance with the illustrated embodiment of the invention by providing a modified finger contact on an otherwise conventional circuit card so that the modified finger contact momentarily contacts two adjacent contacts within the mating receptacle into which the printed circuit card is plugged, thereby momentarily shorting together those two adjacent contacts. This momentary shorting occurs both when the printed circuit card is being plugged into the mating receptacle and when it is removed therefrom to provide the reset pulse required to set the microprocessor in the mainframe to a known state that is protective of both the proper operation and safety of the microprocessor and other electrical components on the printed circuit card and in the mainframe.